1. Field of the Invention
The present invention relates to a display device having a display panel device including a plasma display panel and a functional sheet that is brought into intimate contact with a front surface of the plasma display panel.
2. Description of the Prior Art
Technology development of a plasma display panel (PDP) that is a self-luminous device is directed to a large screen for providing more powerful display. One of the important tasks for a large screen is weight reduction of the panel.
In general, a display device including a plasma display panel has a rigid filter plate having a base of a tempered glass. This filter plate is arranged in front of the plasma display panel with air gap. The filter plate has various functions of adjusting a display color optically, preventing reflection of external light, shielding electromagnetic waves, and shielding near infrared rays concerning displaying operation, and it also has a function of protecting the plasma display panel mechanically.
Arranging the filter plate in front of the plasma display panel is effective for reducing temperature rise in a filter layer due to heat generated in the plasma display panel. Air between the plasma display panel and the filter plate works as a thermal insulator. However, there is a drawback that the heat generated in the plasma display panel may be shut inside an enclosure of the display device, which causes temperature rise of the plasma display panel.
When the plasma display panel becomes high temperature, misdischarge may occur easily. In order to prevent misdischarge, it is necessary to set an upper limit of supplied power to a lower value or to provide a thermal countermeasure such as a high power cooling fan. As quantity of generated heat increases along with the screen size becoming larger, an appropriate thermal countermeasure has to be conducted.
In addition, as the filter plate has a large weight, it is not desired for a large screen of the plasma display panel. In order to reduce a weight of the display device, another structure is suitable in which a thin filter having a base of a resin film is glued directly on the front face of the plasma display panel instead of attaching the filter plate. Japanese unexamined patent publication 2001-343898 discloses a front filter that includes a transparent conductive film for a measure against EMI and a anti-reflection film that is glued on the front side of the front filter.
When a filter is glued on the front surface of the plasma display panel, the filter is apt to be deteriorated due to heat generated by the plasma display panel. As the front surface of the plasma display panel is covered with the filter, heat radiation of the plasma display panel may be impaired. In the conventional structure, however, there was no countermeasure against heat for both the filter and the plasma display panel in a display device in which the filter and the plasma display panel are brought into intimate contact with each other.